The present invention concerns the reduction of solid feedstock comprising metal compounds, such as metal oxides, to form products. As is known from the prior art, such processes may be used for example to reduce metal compounds or semi-metal compounds to metals, semi-metals or partially-reduced compounds, or to reduce mixtures of metal compounds to form alloys. In order to avoid repetition, the term metal will be used in this document to encompass all such products, such as metals, semi-metals, alloys, intermetallic and partially-reduced products.
In recent years there has been great interest in the direct production of metal by reduction of a solid feedstock, for example, a solid metal-oxide feedstock. One such reduction process is the Cambridge FFC electro-decomposition process (as described in WO 99/64638). In the FFC method a solid compound, for example a solid metal oxide, is arranged in contact with a cathode in an electrolytic cell comprising a fused salt. A potential is applied between the cathode and an anode of the cell such that the solid compound is reduced. In the FFC process the potential that reduces the solid compound is lower than a deposition potential for a cation from the fused salt. For example, if the fused salt is calcium chloride then the cathode potential at which the solid compound is reduced is lower than a deposition potential for depositing calcium from the salt.
Other reduction processes for reducing feedstock in the form of cathodically-connected solid metal compounds have been proposed, such as the Polar process described in WO 03/076690 and the process described in WO 03/048399.
Conventional implementations of the FFC and other electrolytic reduction processes typically involve the production of a feedstock in the form of a preform or precursor fabricated from a powder of the solid compound to be reduced. This preform is then painstakingly coupled to a cathode to enable the reduction to take place. Once a number of preforms have been coupled to the cathode, then the cathode can be lowered into the molten salt and the preforms can be reduced. It can be very labour intensive to produce the preforms and then attach them to the cathode. Although this methodology works well on a laboratory scale, it does not lend itself to the mass production of metal on an industrial scale.
It is an aim of the invention to provide a more suitable apparatus and method for the reduction of a solid feedstock on industrial scales.